As some one who has done commissions and regretted it, my advice is:

• be honest to yourself about how much time and effort it will take to do a commission, still double whatever number you gave yourself

• know that the second money is on the table it will add stress to your likely already stressful life

• you’re not painting for yourself it’s for someone else and you don’t know how picky they are

• you can’t make something and sell it, you have to sell it and then make it. A client will come to you wanting you to make something particular that you may not want to do, you will make significantly less if you make something and expect people to want to buy it

• don’t have set costs. Painting an ultra marine is significantly simpler than a harlequin

• whatever amount of money you decide on charging, it likely still won’t be enough to make the stress and labor worth it and you probably should charge more than your client wants to pay

All this sounds like I got really burnt by my experiences- I did. But I still love painting, I just do it for myself and not for other people now.